Method of explosion cladding irregular aluminum objects



Dec. 19, 1967 c. G. A. ROSEN METHOD OF EXPLOSION CLADDING IRREGULARALUMI 'NUM OBJECTS Filed Aug. 5. 1964 5 Sheets-Sheet 1 FIG \B FIGINVENTOR Carl 6. A. Rosen Dec. 19, 1967 c. G. A. ROSEN 3,358,349

METHOD OF EXPLOSION CLADDING IRREGULAR ALUMINUM OBJECTS Filed Aug. 5,1964 S Sheets-Sheet 2 H0: H2 I22 I & |35 134;

INVENTOR Carl 6. A. Rosen Dec. 19, 1967 c. G. A. ROSEN METHOD OFEXPLOSION CLADDING IRREGULAR ALUMINUM OBJECTS 5 Sheets-Shee; 5

Filed Aug. 5. 1964 27 I2 26 2| 4 [U f INVENTOR Carl 6. A. Rosen .FIG IFUnited States Patent 3 358,349 METHQD {3F EXPLGElliEN CLADDING IRREGULARALUMTNUM OBJECTS Carl G. A. Rosen, Woodside, Calif., assignor to DarliteCorporation, Peoria, 111., a corporation of Illinois Filed Aug. 5, 1964,Ser. No. 387,715 13 Claims. (Cl. 29156.5)

This invention relates to an improved method of cladding a cast orforged aluminum body subjected to wide and sudden temperature changesand bodies having nonplanar surfaces with a stainless steel veneer orcladding, and to various products formed thereby.

The term aluminum as used herein encompasses aluminum and aluminum basealloys which contain at least 50% by weight of aluminum, and the termferrous metal embraces iron and alloys thereof including steel andstainless steel. The metallizing metal described herein as molybdenumincludes metals whose boiling point is high enough that a molten spraythereof and its velocity energy directed against the aluminum willvaporize the surface aluminum without such metal reaching its ownboiling point. Such would include cobalt, nickel and titanium.

With internal combustion engines and vehicle brakes used more and morein extremely cold climates, particularly under conditions where thewarm-up period may be fast from 65 F. the internal stresses and strainscan cause shattering where two bonded metals of otherwise desirablecharacteristics but of different coefiicients of expansion are involved.Although, by way of example, pistons made of a single metal wouldsurvive such a short warm-up the use of dual metal pistons is demandedfor the long working time of the piston, in order to attain manywell-known essential advantages including wear surfaces, particularlywith aluminum pistons and brakes. The invention prevents this shatteringwhile further improving piston performance regardless of theconventional head configurations of the piston, whether they be flat orprovided with protuberances or cavities for various purposes.

By way of illustration but not by way of limitation the invention isdescribed primarily with a piston presenting the widest abilities of theinvention. Having in mind a specfic and particularly dlficult to forgepiston body which has a highly rated performance for a multifuelinternal combustion engine, the head of the piston is flat with acentral open cavity into which the fuel is injected for combustion.Generally most conventional surfaces are not designed to have fuelspread in contact with a piston surface, and some are designed toprevent fuel contacting the surface but in the M (Muerer) system thefuel is injected to flow along the wall of a piston cavity generallyreferred to as a shrouded toroidal bowl and presents critical heattransfer control problems to provide high output supercharged engineperformance. In such a piston the wall of the cavity is maintained atabout 600 F. which keeps the liquid fuel contacting it from carbonizingwhile the cyclonic movement in the cavity progressively vaporizes theexposed surface of the liquid and burns it until the cavity becomes dryon the working or power downstroke of the piston. In some of thesepistons an internal closed space in the stock surrounds or partiallysurrounds the cavity to assist in the heat transfer control to maintainthe 600 F.

According to the present invention, the heat conduction through thealuminum piston stock to the piston ring grooves is controlled at theradial faces of the cavity, and a fiat circular heat-conductive shieldis applied to the upper face of the head of the piston to rejectadditional heat into the liquid fuel on the walls of th cavity, as wellas from the head into the combustion chamber. This reduces heataccumulation in and around the piston ring grooves. To assure longevityof the piston ring groove contours under all engine operatingconditions, a preformed solid band of ferrous metal and of appreciablethickness is initially bonded to the upper side wall por tion of thepiston and, thereafter, the ring grooves are radially cut therethrough.

Under ordinary operating conditions, such a band can be satisfactorilyapplied by a thermal shrinkage operation as described in my applicationSerial No. 153,483, filed on Nov. 20, 1961, now Patent No. 3,203,321,and entitled, Method and Product and Bonding Ferrous Metal WithAluminum. However, where extremely low start-up temperatures and highring groove operating temperatures of 500 to 550 F. are experienced, amore effective bond is required. Therefore, according to the presentinvention, a novel method for accomplishing the compressive bondrequired is provided involving the sudden liberation of energy from anexplosive charge by detonation thereof to prestress the aluminum of thepiston under molecular compaction and compression in a directionopposite to its direction of heat expansion and to prestress the ferrousmetal of the band in compaction and tension in a direction opposite toits direction of heat expansion, and, simultaneously therewith todiffusion bond weld them in intimate unoxidized metal-to-metalinterdiffused relationship with high local deformation at the interfaceinvolving a mono layer of particles of a metal such as molybdenum havinga melting point above the boiling point of the aluminum.

By such a method a compacting high impact pressure is applied above thedynamic yield stress of the material transverse to the interface as ashock wave moving parallel to the interface at a velocity above 800 feetper second, but less than the speed of sound in the respectivematerials, to ripple the interfaces and increase the bonding area inorder to assist in the preservation and the maintenance of the bondcompression stresses throughout the bonded area. Some of these stressesinclude shear stresses where portions of the interface ripples aredisposed at a substantial angle to the main face of the bond. Theoptimum speed is from 1000 to 1100 feet per second. Application of theflat circular shield to the upper end face of the piston is made by asimilar explosive process.

The unoxiclized metal-to-metal relationship avoids the formation ofbrittle compounds or alloys and the particle layer, which may be ametallized molybednum spray, is made close enough to the aluminum tovaporize away any surface layer of oxidized aluminum and establish andmaintain an unoxidized aluminum interface. The layer also acts as adiffusion control against undesirable intermetallic compounds developingat the interface.

Thus, a cladding is provided at the ring grooves, the top of the headand around the throat of any cavity where heat differentials and erosionare quite high. The cladding does not break up nor shatter since thestress factor induced remains above the tension factor throughout thefull range of temperature changes and differentials.

The thickness of the ferrous metal on the head is related to the degreeof heat transfer rate or combustion heat desired to be rejected back tothe combustion chamber or envelope. Such increases the effectivcompression ratio, reduces fuel waste, after-burning and crankcasecontamination.

In the accompanying three sheets of drawings pistons having severaldifferent configurations embodying the invention are shown with likenumerals referring to like parts but the description by way of exampleis directed to a particularly diificult design for purposes ofillustrating various considerations of the invention.

In these drawings:

FIGS. 1A through 1F are'sectional views taken substantially centrallyand vertically through bodies constructed in accordance with the methodof the present invention; the first five figs. illustrating contoursmore generally in use for piston heads (FIGS. 1A to FIG. 1B) for diskbrakes, FIG. 1A and drum type brakes (FIG. 1F,

see also FIGS. 7 and ll) FIG. 2 is a sectional view taken substantiallycentrally and vertically through an aluminum piston blank from which thepiston of FIG. 1F is constructed,

FIG. 3 is a fragmentary sectional view similar to FIG. 2 illustratingthe application of a mono-molecular layer of metallized molybdenum tothe upper surface of the piston to provide and preserve nonoxidizedsurfaces thereof where cladding is desired,

FIG. 4 is a fragmentary sectional view similar to FIG. 2 illustratingthe initial application to the upper end face of the piston of anexplosive-charged cladding blank preparatory to detonation thereof.

FIG. 5 is a fragmentary sectional view similar to FIG. 4 showing theexplosive disk operatively applied to the piston blank after detonationthereof,

FIG. 6 is a fragmentary sectional view similar to FIG. 5 illustrating acylindrical body treated by machining thereof to prepare the body forcladding with a circular bandincluding the application of metallizedmolybdenum to the surface,

FIG. 7 is a fragmentary sectional view similar to FIG. 6 illustratingthe initial application of an explosive cladding bandpreparatory todetonation thereof,

FIG. 8 is a fragmentary sectional View similar to FIGS. 6 and 7 showingthe explosive cladding band operatively applied to the body afterdetonation thereof,

FIG. 9 is a representation of a photomicrograph of a section takentransversely through the juncture region between the aluminum and one ofthe cladding elements and in the longitudinal direction of the explosiveforce employed to effect the bonding of parent elements,

FIG. 10 is a sectional view taken centrally and axially through a pistonbody embodying the invention, and

FIG. 11 is a fragmentary sectional view through an showing of the finalstructural character thereof.

The method contemplated by the invention is to provide an aluminum body,preferably forged, and clad it with a wear and heat control metal with abond that will not fracture under extreme temperature changes. The bodyshown for purposes of illustration is a forged aluminum piston bodyhaving a shrouded toroidal bowl in the head thereof and a sealed annularcompartment in the aluminum stock around the bowl, to control the heatconductivity from the bowl to the ring area. A monomolecular layer ofmetallized molybdenum is applied to the exposed aluminum surface to beclad and this is done with the metallizing gun sufiiciently close (2 to3 inches) to vaporize away any aluminum oxides on the surface andexpose, embed in and preserve an unoxidized aluminum interfacetherewith. The molybdenum layer extends over the edge and down andaround a limited portion of the bowl surface whereby surfacetemperatures are controlled so as not to carbonize the injected fuel yetbe adequate to vaporize same for combustion.

Thereupon a blank from a sheet of stainless steel approximately thick iscoated with a wafer of explosive material and one edge is brought torest on one edge of the piston head with the explosive layer out and therest of the blank inclined gradually away from the head face atapproximately an included angle of 3 The powder is preferably, butnotnecessarily, detonated in an atmosphere under a slight vacuum of afew inches of mercury, beginning at the contacting edges. The slightvacuum removes the absorbed layer of air from the mating surfaces toprevent oxide inclusions as a byproduct of the Welding process. Thepowder burns at a rate of slightly less than 1500 feet per second acrossthe rest of the blank, progressively slamming or impacting it againstthe head approximately &

or end face with an interface shock wave of high intensity 1 are therebydiffusion welded and the substrate aluminum 7 stock is found to beprestressed by a compression well above the tension or yield stress ofthe metal over a wide range of temperature changes including -60 F. and600 F.

When the aluminum body is flat or convex as seen in FIGS. 1A to 1C, theweld is complete all the way across but to illustrate the operation uponthe more complex head contour as shown, the sheet metal blooms partiallyinto the bowl and welds down along the edge surfaces of the throat toprotect them from erosion of hot combus tion flame and gases eruptingfrom the bowl immediately following the compression stroke and ignition.The unsupported web of the bloom is later cut away and the clad edgespolished.

Thereafter the blank portions overhanging the side wall of the piston ismachined away and the wall turned down to over the ring groove area. Alike coating of metallized molybdenum is applied for the same reasonsover the machined area and a band of ferrous metal approximately & tothick and defining a frustum of a cone having an included angle of from2 to 5 is slipped over the machined surface with its small diameterleading with a close fit until it comes to rest against a shoulder atthe end limit of the machined area. A layer of like explosive powder isplaced around wardly and contract the ring into a diffusion weld ofunoxidized interface metals with the metallized wall and also with theedge of the head layer of ferrous metal. Thereafter the excess of thering overhanging the head is machined away, the piston is finished toproper size and the piston ring grooves are out. p

The substrate aluminum is prestressed under a compression to a pointabove the yield point of the aluminum in the bonded region throughout atemperature range extending as low as 65 to as high as +550 F. underloaded engine conditions.

More particularly, a forged piston blank 10 is shown in FIG. 2 as havinga fiat head surface 21 representative of all fiat topped pistons and ashrouded bowl 12 generally referred to as a Meurer construction which isrepresentative of any one of a number of different type bowls includingopen sided or shrouded toroidal, concave or hemispherical bowls havingstepped or smooth walls. These numerals with suffix letters identifylike parts throughout FIGS. 1A1E.

In the head stock around the bowl 12 is an annular space 17 formed bymaking a circular groove around the bowl area for oil cooling of thepiston. The stock is upset to close the groove at its upper edges incontacting relationship. Heretofore, this has required argon gas weldingbut this is eliminated by the present invention. The head plate assistsin holding the circular groove in closed relationship. The piston isfinally tooled to the structure of the blank shown in FIG. 10 whichincludes wrist pin bosses 118 and skirtportions 120.

The head of the piston body is faced ofi as shown in V dotted lines inFIG. 2 a distance a little less than its ultimate height and the mouthand throat area of the bowl is finished to an edge face 22, also shownin dotted lines, which has appreciable axial width. Then these surfacesare metallized with molten molybdenum particles 23 sprayed from ametallizing gun 24 as shown in FIG. 3, preferably at a spray distanceappreciably less than 3 when the piston is at room temperature wherebythe heat of the molten particles of molybdenum and their velocityvaporizes away any oxidized surface aluminum and embeds in unoxidizedaluminum. The spray coating 25 is only thick enough to seal the aluminumfrom contact with the air. Generally one pass of the metallizing gunwill sufiice. A monomolecular type coating is desirable. The coatingneed extend own the bowl walls only a slight appreciable distance. Thisuse of the molybdenum greatly reduces the likelihood of an intermediatephase brittle compound being formed at the weld. Slight amounts ofinterface brittle compound may be acceptable with some uses but is notdesirable.

As shown in FIG. 4, a circular disk or blank 26 cut from a metal sheetof desirable thickness from g to 75 thick, preferably stainless steel,is then laid upon top of the head surface 11 with one edge in contact asat 27 and the opposite edge elevated to provide an included angle on theorder of 3 Freferably the blank is coextensive in size with the headsurface. The disk 26 may be held in its elevated position by a prop 28fixed to the piston blank by a suitable frangible adhesive. A charge ofexplosive material 29 in the form of a wafer which is coextensive withthe disk 26 and which burns at a lineal rate less than the speed ofsound in the environmental atmosphere provided is placed on top of theblank 26 and detonated by means of a suitable detonating cap 30 at thecontacting edge. The explosion and shock which follows difiusion weldsunoxidized interface metals as previously described and prestresses orwork hardens the substrate aluminum by compression to an impressivestress above the dynamic yield strength of the metal at -65 F. with aconsistent and predictable value to resist strains to which the bondwill be subjected when the piston is in use at its highest workingtemperature.

In FIG. it will be observed how the blank blooms as shown at 31 into thebowl 12 and bonds marginally to the throat surfaces. The unbonded metalis subsequently cut away and the throat edges are finished off to asharp edged orifice and polished as shown in FIG. 6.

it should be noted that the blank 26 is preferably fiat. However, wherethe piston heads have shallow depressions or protuberances, asubstantially mating contour can be preimposed on the blank but limitedto a space between the two parent parts comparable to the provision ofthe previously mentioned 3 angle. Where the blank is unsupported over adeep depression the blank will bloom with the explosion and bonds at theedge and a short way into the depression to the extent that the blank isupset by the explosion enough to force a compressive shock contactrelationship under the explosive force. This distance depends upon thethickness of the blank, the steepness of the margins of the depression,the relative mildness of the metal in the blank and the force of theexplosion. Within the draw limits of the metal or" the blank, thesefactors can be allowed for and resolved by varying the thickness of thepowder charge over the areas of the depression where bonding is to becontrolled. Moreover where the depression is not to be cladded, theblank can be cut out thereby permitting the marginal edges over thedepression greater freedom to form under the explosion force. Excessmaterial in an unsupported substantial overlap of the blank, however, isevenly sheared off at the edge of terminal support during the weldingprocess. In FIG. 6 the blank 19 is shown as ultimately having the bloom31 removed and the edge of the cavity machined to a sharp orificeopening which will endure under long and hard use of the piston.

The piston ring groove area is machined to a small diameter as indicatedat 33 to receive a stainless steel sleeve 34 such as has been shown FIG.7. Preferably, the machined area 33 is cylindrical, thus providing anupwardly facing annular shoulder 36 at the bottom of the ring groovearea While the sleeve 34 is of frusto-conical design having a smallslant or taper angle on the order or 3". The small base of the conefrustum is such that it may seat upon the annular shoulder 36 and theslant height of the cone frustum is such that the upper rim of thesleeve 34 extends a slight distance above the upper surface of thepreviously applied and explosively deformed d disk 26. Prior toinstallation of the frusto-conical sleeve 34 on the piston blank 10, themachined ring groove area 33 is treated with the metallizing gun 24 toapply a layer of molybdenum thereto for the reasons set forth inconnection with the application of the layer of molybdenum to the wallsof the bowl 12.

A coating or jacket 29 (FlG. 7) of explosive material is applied to theouter surface of the frustoconical sleeve 34- coextensively therewithand is detonated by means of a detonator ring 42 positioned near thesmall base of the cone frustum. Upon detonation, the explosive materialburns progressively upwardly and the violent explosive force thereofcontracts the sleeve 34 against the machined cylindrical piston ringgroove area 33 in a manner similar to that described in connection withthe application of the circular disk 26 to the machine and molybdenumtreated upper end face 21 of the piston blank 10. During the explosion,the frusto-conical sleeve 34 is deformed to a true cylindrical shape,the deformation taking place progressively in an upward direction withthe same phenomena of diffusion welding, scuffing of unoxidizedinterface metals under extremely high pressure, prestressing of thesubstrate aluminum stock, etc, described in con nection with the bondingof the blank 26 to the machined end face 21 as well as to the circularend face of the previously machined blank. Additional physical phenomenaare attendant upon such interface bonding of the stainless steelmaterial of the disk 26 and sleeve 34 to the end face 21 and pistongroove area 33 respectively and these will be described subsequently inconnection with FIG. 9 wherein the physical characteristics of theactual bond effected has been illustrated.

After the frusto-conical sleeve 34 has been applied to the piston blank10 in the manner described in connection with FIGS. 7 and 8, the blankis given a final machining operation wherein the overhanging ring ofmetal above the horizontal plane of the upper face of the deformed disk26 is removed and the annular piston ring grooves are cut completelythrough the sleeve 34 and into the previously machined cylindrical outerface 33 of the piston blank 10. Thereafter the thus machined blank maybe polished or otherwise surface treated to produce the completed pistonshown in FIG. 1. The completed piston retains many of the shapecharacteristics of the original blank 19 as do also the appliedstainless steel cladding and thus, in order to avoid needless repetitionof description, similar reference numerals but of a higher order havebeen applied to the corresponding parts as between the disclosures ofFIGS. 10 and 2. These have been used also on FIGS. 1A1E with sufiixmarks where appropriate.

Referring now to FIG. 10, insofar as the shape characteristics of thepiston 119 are concerned, it is to be noted that the application of thecircular disk 26 to the machined end face 21 of the blank serves toprovide a crown 126 on the top of the piston, this crown including alimited peripheral region occasioned by the overlap of theexplosion-deformed sleeve 34 (FIG. 8). This crown is relieved as at 127where the stainless steel metal enters the bowl 112 and is adhered tothe wall thereof as previously described.

The explosion-deformed sleeve 34 of FIG. 8 establishes a band ofstainless steel around the blank 10 and, when the final machiningoperations previously described are performed upon the blank, this bandis divided into sections numbering two to four depending upon commercialconsiderations. The sections include a relative wide band 134 embracingthe extreme upper regions of the piston head, and narrow bands 134aembracing the land areas between adjacent machined grooves 135. It iswell known in connection with conventional piston operation that thegreatest groove wear takes place in connection with the variouscompression ring grooves and that the oil ring groove which invariablyis disposed below the compres sion grooves does not wear as rapidly.Thus, according to the present invention, only those land areas whichadjoin a compression ring groove 135 are clad with stainless steel, thelowermost groove having no cladding around its lower rim region.Preferably the juncture of the shoulder 36 and sleeve 34 is locatedwhere the lowermost groove is located whereby the cutting of the groovecleans up any minor discrepancies and flaws that might possibly haveoccurred in the explosion welding step.

Explosion welding as a name is not new, and explosives have been used invarious Ways as quick sources of power to impel impacts betweenelements. Although the term explosion Welding can be used in referringto the present invention the method of the present invention is novel inbonding dissimilar metals such as steel and aluminum with non-oxidizedinterface metals under a washing and sending impact which inducesplastic flow of the joining surfaces and which interlocks and diffusionbonds the metal under a compression which is not relieved over wideranges of temperature changes. The explosive force is appliedprogressively along the bonding area with a rapid compression andexpansion of the two elements and this results in the attainment of amore intimate bond between the metals to be joined together than hasheretofore been possible.

Additionally, the preliminary treatment with metallized molybdenum sprayof the area of the aluminum metal to which the cladding metal is appliedimmediately prior to explosive application of the cladding assuresnon-oxidized metal interfaces with molybdenum particles that can movewith the action of the metal at the bonding surface during theexplosively applied force to maintain a more perfect union between thebase and cladding metals. Furthermore, the progressive burning of theexplosive material, coupled with the application of a metallizedmolybdenum coating, makes it unnecessary to etch or otherwise roughenthe surfaces undergoing welding at the interface as has been consideredadvantageous practice heretofore.

While the precise chemical and physical phenomena involved in connectionwith the present process may not be entirely understood, therepresentation of FIG. 9 which is taken from an actual 500 powermicrophotograph of a section taken transversely through the interfacebetween a portion of a piston and its cladding shows the rippling orwave action attained. Considering this microphotograph representation inconjunction with FIGS. and 8, it is to be noted that since detonationinitially takes place on the cladding blank 26 at one extremity thereofwhich is in contact with the aluminum body it and ignition of theexplosive material 29, progresses along the cladding in its direction ofdivergence between the body and blank, the blank is progressivelyslammed and scufied into contact with the base metal as indicated indotted lines in FIGS. 5 and 8 as a shock wave action. Fusing of the twometals at the interface takes place, not only as a result of the heat ofthe exploding powder, but also as the result of three other factors,namely the outrush or expressing of air from between the base metal andthe blank controlled in amount by the partial vacuum; the slammingimpact which, although of a progressive scuffing or plastic flow of themetals, is nevertheless appreciable and the heat of molecular compactionof the metals. A certain amount of heat is created by compression andthe outrush of air with friction against the metals at the interface.However, the predominant force for making the bond is the heat generatedby the pressure wave compacting the molecules of the metals at theinterface with a rebound and reestablishment of pressure contact as avibratory action of microsecond duration. The compaction impact createsheat when it strikes a steel target and a rippling action follows whichassures the bond when the explosive charge approaches but does notexpend a crushing blow. The combined heat resulting from these phenomenacreates sufiicient heat to effect melting of the two metals at theinterface and a displacement and diffusion of molecules at theinterface.

As to the intimacy of the bond which is created at the interface, anon-oxidized union between the metals at the interface and resultingfrom the use of the metallized molybdenum spray is, of course, conduciveto an intimate union. What is equally important however is thephenomenon which obtains when interfacial turbulence is created by thepassage of one fluid media forcibly across the surface of another fiuidmedia. Waves on the surface of a body of water initiated by a windstrong enough to cause white caps are not truly sinuous waves but ratherthey have gradual curvature on their trailing sides and sharply curvedcavities on their leading sides. Stated othewise, the waves of windblown Water lean forwardly as their base is retarded by the frictionalinertial drag of the main body of water. Such a wave pattern isillustrated in FIG. 9 wherein a wave pattern is established at theinterface between the aluminum piston blank 10 and a blank 26.Individual waves 140 are created due to the outrush of air and movementof molten metal between the body and blank and these waves haverelatively sharp cavities 142 along their leading edges. These cavitiescreate interlocks between the two metals and enhance the bondtherebetween. This is a characteristic representing the establishment ofa good weld.

Articles constructed according tothe above-described method and asexemplified by the piston 110 of FIG. 10 are capable of withstandingsudden and extreme temperature changes ranging from as low as 65 F. toengine operating temperatures as high as 550 F., the bond between thebase metal of the piston body and the cladding remaining intact andunder compression, particularly at the annular surfaces throughout therange of heat expansion. When it is considered that the variousphenomena which take place as a result of the explosion lasts on theorder of only microseconds, it will be appreciated that the explosiveforce is not a gradual compressive force such as might be the case ifthe sleeve were compressed under the influence of pressing dies. Ratherthe compressive force is an impact force which hammers the extreme outersurface region of the sleeve to a density not transmitted through theentire sleeve thickness and this dense surface skin which is created onthe sleeve not only is extremely wear resistant, but 1t also places thesleeve under tension and provides a permanent centripetal force inwardlyagainst the piston body. The piston therefore possesses greater wearcharacteristics than that of a piston which is similarly clad byconventional shrinkage or other methods.

By way of example with a blank 1 thick of 1010 steel upon a flat surfaceof a body of 4032 aluminum alloy disposed at an angle of 2% to eachother, an explosive sheet of Dupont EL 506-D sheet explosive between 35and 40 mils thick and detonated by a P-L-H or equivalent detonator willimpart a velocity of 25 to 35 IIIH'L/pSCC. to the blank which results ina collision point velocity from 3.35 to 4.0 mm./,usec. and produce aweld that withstands without deterioration rapidly repeated temperaturechanges between 65 F. and 550 F. occurring within as little as fifteenminutes.

The explosive preferably is preformed in rings of a low cost castableexplosive such as composition B (60% RDX and 40% TNT). Other explosivessatisfying the suggested burning rate may be used and the amount usedincreases with the thickness of the applied cladding within thevelocities indicated. Even then less than a pound would be required for12 square inches of stainless steel thick.

In this connection a much larger area is involved with brake drumbraking areas and it has been found that a slight modification of thestep shown in FIG. 7 provides a capability of bonding against even widerranges of temperature such as are experienced with vehicle brakes. Inperforming the process with brakes, an aluminum bake drum 210 taperedslightly on its outer sur- 7 face 240 is wedged into a correspondinglytapered ring anvil member 241 having ejection pins 248 therein. Theperiphery 243 of the ring anvil supports the skirt of the brake drumagainst the force of the explosive used. The working face 221 of thedrum is machined to 8. cylindrical contour having an annular groove 244bordering its inner edge and sprayed with a molecular layer ofmolybdenum 225 in the manner and for the purposes already described.

The liner member 234 is made from ductile mild steel as an integral unitand is formed as a frustrum of a cone having a taper angle of 3. Themajor diameter is slightly less than the diameter of the working face225 of the brake drum and preferably for ease of insertion is disposedat the skirt edge of the brake drum with edge 245 at the minor diameteroverlapping the groove 244. An explosive band 229 is laid against theinside face of the liner 234 with a detonator ring 242 at the edgehaving the major diameter.

Thereafter, the detonator is fired, and the explosion bonds the liner tothe molybdenum coated face 225 with the inner edge at 245 driven intointerlocking relationship with the groove (FIG. 1F). The drum is ejectedfrom the ring anvil 241 and the skirt edge and braking surface aremachined to their final form. The product not only has a bondedinterface relationship under molecular compression which is not relievedwithin the ranges of temperature changes experienced under workingconditions but high heat conductivity of the bond with a thin bearingliner dissipates the heat at an improved high rate to preventdeterioration of the liner. Moreover, in the embodiment shown theexpansion tendency of the liner under brake pressure is in the directionfavorable to the re tention of the bonded relationship when heat isbeing generated at a high rate.

In all instances attenuators are attached to the explosive charges toestablish the explosion reaction pressure and direct the workingpressure against the blank for welding. The attenuator (not shown) maybe a piece of cardboard blotter or thin rubber film between the powderand applied member that varies the rate of pressure rise of theexplosion to control the sharpness of the blow on the anvil to providemore closely a sine wave effect.

Various modifications and variations of the present process may be madewithout departing from the spirit and scope of the present invention asdefined in the appended claims.

The invention is not to be limited to the exact arrangement of partsshown in the accompanying drawings or described in this specification asvarious changes in the details of construction may be resorted towithout departing from the spirit of the envention. Neither is theinvention to be limited to the exact sequence of method steps set forhherein since they too may be varied within the scope of the invention.For example, whereas in FIG. 7 the confronting surfaces of the pistonblank 10 and sleeve 34 are shown as being divergent at an angle on theorder of 3 by reason of the frusto-conical shape of the sleeve, it iswithin the purview of the invention to employ a cylindrical sleeve andto machine the piston ring groove area 33 of the blank 10 on an upwardlytapering bias so that the 3 angular divergence between the confrontingsurfaces will be preserved. The 3 angle may be changed to a lower angleif a lower velocity powder is developed. Also, the sleeve can be weldedbefore application of the blank if desired. Additionally, while themethod set fort-h herein has by way of example been described inconnection with the cladding of a generally cylindrical piston blankwith various head configurations, the method may, by suitabledimensional modifications as desired, be employed for the cladding ofcylindrical and flat objects having rapid and wide temperature changes,such as cylindrical or disk type vehicle brake members where heatdissipation is also important, within the spirit of the invention, thescope of which is commensurate with the appended claims.

What is claimed is:

1. The method of cladding a predetermined surface area of an aluminumobject with a substantially rigid ferrous metal veneer of appreciablethickness by a progressive impact welding operation involving therippling and interface fusion of the metals, comprising: metalizing saidsurface area with a metal whose melting point is above the boiling pointof the aluminum positioning a sheet of the veneer metal having a surfaceshaped conformably to said metalized surface area and with said shapedsurface confronting said surface area and in close proximity thereto anddiverging therefrom so as to provide an included angle on the order of 3with the apex thereof within the confines of said surface area, anddetonating an explosive thereafter applying pressure progressivelyacross an exterior surface of said sheet of veneering metal commencingat said apex to thus exert a rolling plastic flow on the sheet in thedirection of divergence between said surface area and confrontingsurface to impart a progressive movement of the sheet into impactingrelationship against the aluminum object under motivating pressuresufiicient to express the air from be tween the sheet and object at arate sufficient to generate appreciable heat of friction and displacethe metalizing metal as a diffusion control against undesirableintermetallic compounds developing at the interface, and also sufiicientto generate appreciable heat of impact between the metals, with thecombined heat thus generated being sufiicient to melt both the aluminumand ferrous metals at their interface region of union whereby anon-oxidized bond is established at the interface under a compressionbetween said both metals which is not relieved over wide ranges oftemperature changes.

2. The method set forth in claim 1, wherein the predetermined surfacearea of the aluminum object is cylindrical and the sheet of veneeringmetal is in the form of a frusto-conical sleeve having a slant angle onthe order of 3 and having one of its base diameters substantially equalto the diameter of the surface area, the sleeve being held intelescoping relationship with respect to the cylindrical surface area atthe time of the application of impact pressure thereto.

3. The combination called for in claim 2 wherein said one of the basediameters is the major diameter and the method includes externallysupporting said aluminum object against expansion during detonation ofsaid explosive.

4. The method set forth in claim 2 wherein said one of the basediameters is the small diameter.

5. The method of cladding a predtermined surface area of an aluminumobject with a substantially rigid ferrous metal veneer of appreciablethickness by a progressive impact welding operation involving therippling and interface fusion of the metals, comprising: spraying saidsurface area with an oxidation-inhibiting substance whose melting pointis above the boiling point of the aluminum positioning a sheet of theveneer metal having an inner surface shaped conformably to said sprayedsurface area and with said shaped surface confronting said surface areaand in close proximity thereto and diverging therefrom so as to providean included angle on the order of 3 with the apex thereof within theconfines of said surface area, and detonating an explosive against theouter surface of said veneer metal and thereby applying pressureprogressively across an exterior surface of said sheet of veneeringmetal commencing at said apex to thus exert a rolling action on thesheet in the direction of divergence between said surface area andconfronting surface to impart a progressive movement of the sheet intoimpacting relationship against the metal object inducing plastic flow ofthe metals under motivating pressure sufficient to express the air frombetween the sheet and object at a rate sufficient to generateappreciable heat of friction, and impact to melt and scuif theunoxidized interface metals and displace and diffuse saidoxidation-inhibiting substance in a non-oxidized union therewithcontrolling against undesirable intermetallic compounds developing 1 1at the interface whereby the metals are bonded under compacting pressureabove the dynamic yield stress of the materials which is not relievedover wide ranges of temperature changes.

6. The method set forth in claim 5, wherein the object is a forgedaluminum piston, the metal of the veneering is ferrous metal, andwherein the confronting surface to which the oxidation-inhibitingsubstance is applied is the surface area of the metal object.

7. The method set forth in claim 5, wherein the oxidation-inhibitingsubstance applied to said one confronting surface is a mono-molecularlayer of metallic molybdenum.

8. The method set forth in claim 5, wherein the oxidation-inihibitingsubstance applied to said surface area is metallic molybdenum andwherein its application is made by the spraying of said surface with agaseous suspension of metallic molybdenum particles.

9. The method of cladding a predetermined contoured surface area of analuminum object with a substantially rigid metal veneering ofappreciable thickness by a progressive explosion-initiated impactwelding operation involving the interface fusion of the metals,comprising: metalizing said surface area with a metal whose meltingpoint is above the boiling point of the aluminum positioning a sheet ofthe veneering metal having a surface shaped conformably to the contourof said surface area with such surface confronting said surface area inclose proximity thereto and diverging therefrom so as to provide anincluded angle on the order of 3,placing a coating of an explosivesubstance on an exterior surface of the sheet and in effectivecoextensive register with the interface area to be fused, detonatingsaid explosive'subarea to thus apply impact pressure to said sheetprogressively as burning of the explosive substance progresses in thedirection of divergence of the confronting surfaces and exert a rollingaction on the sheet in such direction and move the same into impactingrelationship against the metal object under motivating pressuresuflicient to express the air from between the sheet and object at a isnot relieved over wide ranges of temperature changes.

10. The method set forth in claim 9, wherein the predetermined surfacearea of the aluminum object is cylindrical and the sheet of veneeringmetal is in the form of a frusto-conical sleeve having a slant angle onthe order of 3 and having a small base diameter substantially equal tothe diameter of the surface area, the sleeve being placed in telescopingrelationship with respect to the cylindrical surface area immediatelyprior to detonation of the explosive substance.

stance at its region of closest proximity to said surface 11. The methodset forth' in claim 9, wherein the predetermined surface area of thealuminum object presents a continuous closed outer band-like contour andthe sheet fof veneering metal is in the form of a sleeve, the sleevebeing placed in telescoping relationship with respect to the cylindricalsurface immediately prior to detonation of the explosive substance sothat all circumferential regions of the sleeve an included angle on theorder of 3 between the inside surface of the sleeve and thepredetermined surface area of the metal object is maintained.

12. The method of cladding a predetermined surface area of an aluminumbody element with a mono-molecular film of metalized molybdenum thereinwith a ferrous metal veneer of appreciable thickness comprisingpositioning a substantially rigid sheet element of the veneer having asurface shaped conformably to said surface area disposed in closeproximity thereto and diverging therefrom to define anvincluded angletherewith on the order of 3 with the apex thereof within the confines ofsaid surface area, driving said sheet element at a velocity within theapproximate range of 25 to 35 mm./ .t seconds progressively in adirection away from said apex along the face thereof opposite to saidshaped surface to progressively collide said sheet element against saidbody with extreme shock at a collision point velocity within the rangeof substantially 3.354.0 mmj seconds and thereby express the air betweenthem and generate a surface melting heat to ripple the interfaces of theelements in bonded molecularly displaced and diffused relationship withthe metalized molybdenum over a bonding interface area than the initialarea defined by the elements within said included angle whereby themetals are bonded under compacting pressure above the dynamic yieldstress of the bonded materials which is not relieved over a range oftemperatures from F. to +550 F.

13. The process defined in claim 12 including cutting through a limitedarea of said veneer and placing an element in said cut in heat exchangecontact directly with the aluminum of said body.

References Cited UNITED STATES PATENTS Chudzik 29 -486 JOHN F. CAMPBELL,Primary Examiner.

J. L. CLINE, Assistant Examiner.

12. THE METHOD OF CLADDING A PREDETERMINED SURFACE AREA OF AN ALUMINUMBODY ELEMENT WITH A MONO-MOLECULAR FILM OF METALIZED MOLYBDENUM THEREINWITH A FERROUS METAL VENEER OF APPRECIABLE THICKNESS COMPRISINGPOSITIONING A SUBSTANTIALLY RIGID SHEET ELEMENT OF THE VENEER HAVING ASURFACE SHAPED CONFORMABLY TO SAID SURFACE AREA DISPOSED IN THE CLOSEPROXIMITY THERETO AND DIVERGING THEREFROM TO DEFINE AN INCLUDED ANGLETHEREWITH ON THE ORDER OF 3* WITH THE APEX THEREOF WITHIN THE CONFINESOF SAID SURFACE AREA, DRIVING SAID SHEET ELEMENT AT A VELOCITY WITHINTHE APPROXIMATE RANGE OF 25 TO 35 MM./$ SECONDS PROGRESSIVELY IN ADIRECTION AWAY FROM SAID APEX ALONG THE FACE THEREOF OPPOSITE TO SAIDSHAPED SURFACE TO PROGRESSIVELY COLLIDE SAID SHEET ELEMENT AGAINST SAIDBODY WITH EXTREME SHOCK AT A COLLISION POINT VELOCITY WITHIN THE RANGEOF SUBSTANTIALLY 3.35-4.0 MM./$ SECONDS AND THEREBY EXPRESS THE AIRBETWEEN THEM AND GENERATE A SURFACE MELTING HEAT TO RIPPLY THEINTERFACES OF THE ELEMENTS IN BONDED MOLECULARLY DISPLACED AND DIFFUSEDRELATIONSHIP WITH THE METALIZED MOLYBDENUM OVER A BONDING INTERFACE AREATHAN THE INITIAL AREA DEFINED BY THE ELEMENTS WITHIN SAID INCLUDED ANGLEWHEREBY THE METALS ARE BONDED UNDER COMPACTING PRESSURE ABOVE THEDYNAMIC YIELD STRESS OF THE BONDED MATERIALS WHICH IS NOT RELIEVED OVERA RANGE OF TEMPERATURES FROM -60*F. TO +550*F.